Pretty sure Tom Griebe over on the Facebook page has responded to questions re trailer locks in some detail... sounded like he knew what he was talking about, at least as it applied to UHaul
CT's and similar. [I'm still new to using the 'search' feature very well, or I'd try to find his post
Perhaps that helps?......
Went back and tried the search just now. This is one out-take from it:
As noted, the L300 lock is not made anymore and used ones are super expensive. A locksmith can easily make a new key and clean up an old lock. Worst case, there are other manufacturers that make a lock similar enough to the L300 that it can be replaced. Google "Bargman L300 replacement ".